You want to adjust your shell environment to account for the way you work, your physical location, your language, and more.
See the table in the section “Adjusting Shell Behavior Using set, shopt, and Environment Variables” in Appendix A.
There are three ways to adjust various aspects of your environment. set is standardized in POSIX and uses one-letter options. shopt is specifically for bash shell options.
And there are many environment variables in use for historical reasons, as well as for compatibility with many third-party applications.
How you adjust what and where, can be be very confusing. The table in the section “Adjusting Shell Behavior Using set, shopt, and Environment Variables” in Appendix A will help you sort it out, but it’s too big to duplicate here.